Freshness of beef or other meat is an important factor in quality control in a meat distribution process, or in a meat supply business. There have been proposed various methods or apparatus for measuring the freshness of meat. One of such apparatus is a meat freshness measuring apparatus described in Japanese Patent Laying-Open No. 1-156664. According to this Japanese Patent Document, it was made clear by studies of Saito et al (Transactions of the Japanese Society of Scientific Fisheries, Vol. 24, pp. 749-750: 1957) and Uchiyama, Ehira et al (Transactions of the Japanese Society of Scientific Fisheries, Vol. 36, pp. 177-187, 977-992: 1970) that a composition ratio of nucleic acid compounds contained in beef or other animal meat has a close relation with freshness. More specifically, since ATP (adenosine triphosphate) in beef or other animal meat decomposes, after the death, in the order of ATP.fwdarw.ADP (adenosine triphosphate).fwdarw.AMP (adenosine monophosphate).fwdarw.IMP (inosinic acid).fwdarw.Hx R (inosine).fwdarw.Hx (buxanthine), the following K value is used as an index of freshness. EQU K value (%)=(H.times.R+Hx)/(ATP+ADP+AMP+IMP+H.times.R+Hx).times.100.
In addition, it was found as a result of the study by Watanabe et al (Papers on Polymers, Vol. 41, pp. 233-248: 1984) that ATP and ADP decompose rapidly after death, and that there is a very small quantity of AMP. Thus, it was found that there is no practical problem if the terms of ATP, ADP and AMP are omitted from the above-mentioned expression K value.
The K value has been conventionally measured by various methods such as a column chromatographic method (Kato et al, Transactions of the Japanese Society of Scientific Fisheries, Vol. 39, pp. 1039-1044: 1973), an oxygen method (Uda et al, Japanese Patent Publication No. 59-130200), and a sensor method (Watanabe et al, Japanese Patent Publication No. 59-107256, or Arai et al, Japanese Patent Publication No. 59-232097).
Another method conventionally used is a spectral method utilizing reflected or transmitted light, in which conditions of a meat pigment can be directly detected. Thus, this method is useful for determining what influence the handling and processing of meat exert on the stability of the meat pigment. For this method an application of a laser beam may be considered. However, measuring apparatus using this method are suited for use in laboratories but not suited for practical use in meat processing factories.